Units Definition: The standard measure of each kind of physical quantity is called a UNIT. Measurement: Measurement implies comparison with a standard value. The magnitude of a physical quantity can be written as: Numerical ratio x Units

Types of Units In Science and Engineering there are tow kinds of Units: Fundamental Units Derived Units  Units to measure Length, Mass and Time are known as Fundamental Units.  All other units which can be expr3esseed in terms the fundamental units are called Derived Units.

Dimension Definition: The unique quality of every quantity which distinguishes it from all other quantities is called dimension. Dimensional symbols for Length, Mass and Time are: L, M, T All Derived units would be defined as multiple of fundamental dimensions: Volume….L 3 Speed …..LT -1 Acceleration …..LT -2

System of Units British System of units describes fundamental in centimeter, grams and seconds and therefore called CGS system. The System that uses Meter, Kilogram and Second is called MKS. International System of Units…SI mostly uses MKS units but is rationalized in application.

Types of SI SI units are divided into Three: Base Units Derived Units Supplementary Units

Base Units Quantity;Name:Symbol: Lengthmetrem MasskilogramKg Timeseconds Electric currentampereA Thermodynamic temperaturekelvinK Luminous intensitycandelacd Amount of substancemolemol

Derived SI Units… 1 Quantity:Name:Symbol: AreaSquare metrem2m2 VolumeCubic metrem3m3 SpeedMetre per secondm/s AccelerationMetre per second square m/s 2 DensityKillogram per cubic metre kg/m 3

Derived SI Units…..2 Quantity:Name:Symbol: Concentration of massMole per cubic metre mol/m 3 Activity1 per secondS -1 Specific volumecubic metre per killogram m 3 /kg luminancecandila per square metre cd/m 3

SI derived units with special names QuantityName:Symbol : In form of other units In form of SI units FrequencyhertsHz-s -1 ForcenewtonN-m.kg.s -2 PressurepascalPaN/m 2 m -1.kg.s 2

SI derived units with special names QuantityName:Sym- -bol: In form of other units In form of SI units EnergyjouleJN.mm 2.kg.s -2 Radiant fluxwattWJ/sm 2.kg.s -3 Electric charge coulombCA.ss.A Electric tension voltVW/Am 2.kg.s -3.A -1

SI derived units with special names QuantityName:Sym-- bol: In form of other units In form of SI units capacitancefaradFC/Vm 2.kg -1.s 4 Electric resistance ohm  V/Am -2.kg.s -3.A -2 ConductancesiemensSA/Vm -2. kg -1. s 3. A -2

SI derived units with special names QuantityName:Symbol : In form of other units In form of SI units Magnetic fluxweberWbV.Sm 2.kg.s -2.A -1 Flux densityteslaTWb/m 2 Kg.s -2.A -1 InductancehenryHWb/Am 2.kg.s -2.A -2 Luminous fluxlumenlm-cd.sr

Definition related to Instruments True or actual Value: That magnitude to measuring system which can be approached and never evaluated is termed as True Value. Indicated Value: The value which is indicated by the instrument. Correction: The revision applied to the critical value so that the final result obtained improves the worth of result is called correction. Overall error: The difference of sacle reading and true value. Range: The region between the limits an instrument can operate.

Definition related to Instruments Sensitivity: The ratio of output response to a specified change in the output is called sensitivity. Minimum measurable change in variable is called Resolution sensitivity. Lowest level of measured variable that produces effective response is called Threshold sensitivity. Scale Sensitivity: The ratio of change in scale to corresponding change in pointer deflection. Scale Readability: